Microwave expansion of tobacco

ABSTRACT

A process for puffing tobacco leaf in whole or cut form is disclosed in which the tobacco is impregnated with a suitable liquid, such as water, and then introduced into a water vapor containing zone wherein the tobacco is subjected to exposure to a microwave field to vaporize the water in the tobacco expanding the cells and thereby puffing the tobacco.

" nited States Patent 1191 Laszlo MICROWAVE EXPANSION OF TOBACCO TiborS. Laszlo, Richmond, Va.

Philip Morris Incorporated, New York, NY.

Jan. 22, 1973 Inventor:

Assignee:

Filed:

Appl. No.:

us. 01 131/140 P, 131/121 Int. Cl A24b 3/18 Field ofSearch 131/121,140144 [56] References Cited UNITED STATES PATENTS 5/1952 Sowa 131/140 P8/1956 Heljo 11/1968 delaBurde ..l3l/l40P 2/1969 Hindetal. 131/121 STEPrimary ExaminerMelvin D. Rein Attorney, Agent, or Firm-WatsonLeavenworth Kelton & Taggart 5 7 ABSTRACT A process for puffing tobaccoleaf in whole or cut form is disclosed in which the tobacco isimpregnated with a suitable liquid, such as water, and then introducedinto a water vapor containing zone wherein the tobacco is subjected toexposure to a microwave field to vaporize the water in the tobaccoexpanding the cells and thereby puffing the tobacco. 1

12 Claims, 2 Drawing Figures AM N STEAM OUT WAVE IN WAVE OUT MICROWAVEEXPANSION OF TOBACCO BACKGROUND OF THE INVENTION The desirability ofexpanding tobacco for use in smoking products is well-known, tobacco inexpanded form having, inter alia, for a given weight thereof a greaterfilling capacity than regular tobacco, and in some instances a lowerresistance-to-draw (RTD) as well as other advantageous characteristics.Certain manners of expanding tobacco are well-known. Thus, tobacco hasbeen expanded by impregnating it with certain volatile materials orblowing agents, and then applying heat to cause puffing, the latterbeing facilitated in some instances by a reduction of the externalpressure acting on the tobacco. lmpregnants used in such processesinclude water, organic solvents, ammonia, carbon dioxide, andcombinations of the last two. Of these the simplest and most desirablein terms of cost, availability and absence of need for removal from theproduct following puffing is water. The use of water to puff tobaccostems in conjunction with applying energy in various forms to causerapid heating and hence expansion is described in detail in US. Pat.Nos. 3,409,022; 3,409,023 and 3,529,606.

However, the expansion of tobacco leaf, whole or cut, with waterimpregnant by such means as provided in the patents aforesaid does notprovide a commercially optimal puffing procedure for leaf tobacco. It isbelieved the ready permeability of the leaf structure to water permitsescape before substantial puffing can take place. Since the tobaccoexpansion process is based on generating elevated pressure in thetobacco cell walls at a suitable rate, the rate of vaporization has tobe greater than the diffusion of the vapors through the cell walls, butthe maximum resulting pressure has to be less then the bursting strengthof the cell structural elements. Accordingly, while such knownprocedures are satisfactory for puffing stems wherein permeability issatisfactorily low, the said known procedures are not effective forpuffing leaf tobacco. The alternative procedure of effecting tobaccoexpansion with water alone, through freeze-drying, while well-known is acomparatively slow and expensive approach.

In the convection heating or mass transfer (so-called tower" procedures)and radiant transfer (infrared) expansion methods, the energy requiredfor the heating of the liquid to vaporize same is deposited at theoutermost surface of the cut "tobacco and only reaches the impregnatingliquid by thermal conduction through the tobacco cell walls.Accordingly, the rate of vapor generation is controlled by the rate ofenergy delivery at the tobacco surface and by the thermal conductance ofthe cell wall. Generally to effect vaporization at the requisite rate, ahigh rate of energy delivery at the tobacco surface is required so thatin effecting energy transfer in both aforementioned expansion processes,the outer surface of the tobacco reaches an unnecessary, and in manycases, harmfully high temperature.

The principles of application of a microwave field to tobacco forvarious purposes and with various consequences thereto including acertain resultant puffing are known. The use of a microwave field onmoisturecontaining tobacco for the purpose of puffing stems also isknown, being described, e.g., in US. Pat. No. 3,409,023. Techniques forpuffing as described in the last-mentioned patent as generally knowninvolving microwave field application are not commercially feasible forpuffing leaf tobacco principally because they involve prolonged exposureof the tobacco to the microwave field and the degree of expansionachieved with leaf by such known techniques is insufficient toaccomplish a satisfactory increase in the filling power of the tobacco.

SUMMARY OF THE PRESENT INVENTION The present invention relates to theapplication of a microwave field to tobacco leaf containing moisturewhile the latter is in an environment saturated or nearsaturated withwater vapor to therewith cause a significant degree of puffing orexpansion of the tobacco. The exposure of the tobacco to such form ofenergy is very short so that a high through-put is possible therebyproviding an effective and commercially optimal manner of expandingtobacco.

In a suitably selected oscillating electromagnetic (microwave) field,the energy coupling (transfer) occurs preferentially between the fieldand certain liquids in some solids. The solid structure does not heat upat all, or only through conductance from the heated liquid. Under thesecircumstances, not only will the greater fraction of the invested energybe used for the heating (vaporization) of the liquid but the temperatureof the solid will lag considerably behind that of the liquid.

In accordance with the present invention, leaf tobacco in whole leaf orcut filler form is impregnated with a suitable aqueous liquid impregnantsuch as water alone or a salt solution to provide a' total basis weightof liquid of at least 20 percent and the impregnated tobacco is thenintroduced into a water vapor containing zone wherein the tobacco isexposed to microwave energy, i.e., a microwave field, to vaporize thewater in the tobacco at a rate and pressure which expands the cell wallsof the tobacco and causes puffing of the same. Preferably the treatmentof the tobacco is effected in a suitable microwave applicator on acontinuous basis involving transporting the tobacco through theapplicator in a predetermined period of time on a suitable travelingbelt. For the purpose of providing a water vapor environment in themicrowave applicator, the same can be provided with connection to asource of saturated steam and further it is preferable that thetemperature condition in the zone be equilibrated to a temperature inthe range of about C. to C. As an incident to the evaporation of liquidfrom the impregnated tobacco, any condensate consequent therefrom, aswell as from the presence of steam in the applicator, can be andpreferably is removed.

The achievement of puffing of leaf in the manner provided by the presentinvention is believed to occur for the following reasons. The competingroutes for re lease of pressure resulting from vaporization of moisturewithin the cell wall are expansion and diffusion to the surroundings.The first is a function of. the overall pressure difference, the lattera function of the water vapor partial pressure difference. To minimizethe second route, the external water vapor partial pressure must besubstantially increased without increasing the total external pressureas by saturation of the surrounding atmosphere. A desirable lower limitis 40 percent water vapor by volume pressure).

For the purpose of generating a microwave field, a

microwave fringing field applicator of known construction can beemployed, being used in conjunction with a thermally resistant glass orlow loss factor glass hood enclosure which defines the zone wherein thepuffing is effected with suitable connections for inlet and outlet ofsteam being provided on the hood.

Tobacco leaf, either in whole or cut filler form treated in accordancewith the present invention, has enhanced puffed characteristics on theorder of up to 50 percent or more expansion of the puffed product overthe raw tobacco, while at the same time such treatment is carried out inshortened time periods on a continuous basis to thereby provide acommercially feasible manner of puffing leaf tobacco with a microwavefield.

BRIEF DESCRIPTION OF THE DRAWINGS A fuller understanding of the natureand objects of the present invention will be had from the followingdetailed description taken in conjunction with the accompanying drawingshowing by way of example preferred embodiments of the inventive conceptand in which:

FIG. 1 is a diagramatic depiction of the apparatus and process by whichleaf tobacco can be expanded in accordance with the principles of thepresent inventlon.

FIG, 2 is a microwave fringing field applicator which is employed in theapparatus depicted in FIG. 1 for generation of a microwave field.

Throughout the following description, like reference numerals are usedto denote like parts in the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention isconcerned with the puffing of tobacco leaf and while it will bedescribed in embodiments thereof as used for puffing cut tobacco leaffiller, it will be understood that the invention is equally applicableto the puffing of leaf tobacco in whole leaf form.

In accordance with the present invention, the leaf tobacco to be puffedfirst must be treated with a suitable aqueous liquid to impregnate thetobacco so that it has a moisture content, expressed as oven-volatiles"in the range of about 20 to 60 percent total weight basis. Tobaccocontains about 2 percent of volatile matter other than water which islost in the test for oven volatiles (O.V.), but from a practicalstandpoint, at moisture levels above l percent in tobacco O.V. may beregarded as substantially equivalent to moisture and is used herein inthat context. The O.V. test is used because of its ease and rapidity inpreference to water analysis. Preferably the impregnant should amount toabout 40 percent of the total basis weight of the tobacco. Asimpregnants water, as well as salt solutions, are particularlyeffective. Where salt solutions are used, the same preferably are in theform of a sodium chloride solution in a range of about 0.1 to 0.7 molNaCl. After the tobacco has been suitably impregnated or moistened to arequisite or desired level, the tobacco is ready for processing in theapparatus depicted in FIG. I, the tobacco in whole leaf or cut fillerform being deposited in a feed bin or hopper 12 designed to continuouslyfeed tobacco to the processing apparatus. The apparatus includes a beltconveyor 14 which in one form can be comprised of a resin impregnatedwoven glass fabric and which transits an endless course through themicrowave field applicator depicted generally at 16. Desirably the beltconveyor 14 is made of woven glass fabric impregnated with a polymer oflow loss factor, the belt thus being substantially electricallynon-conductive and not subject to heating to maximize the amount ofthermal energy generated in the tobacco. The microwave applicator unit16 includes a microwave field generating component 18 known as afringing field applicator and manufactured by Genesys Systems, Inc.,Palo Alto, Calif. The microwave applicator unit 16 further includes thecustomary cut-off tubes 20 which function to confine the presence of themicrowave field to the zone in which the tobacco is to be treated andwhich zone is defined by a hood like enclosure 22, the hood enclosure 22being preferably provided in the form of a low loss factor glass hood orenclosure having in association therewith a microwave field reflectingelement in the form of a metal cage.

As a preliminary to puffing the tobacco, the microwave applicator unit16 has the temperature condition in the zone thereof defined by hoodenclosure 22 equilibrated to a temperature in the range of about C. toabout l50C. Furthermore, the puffing of tobacco in accordance with thepresent invention involves the provision of a water vapor containingzone inside the microwave applicator and for this purpose as well as forthe purpose of equilibrating the temperature therein, saturated steam isintroduced into the hood enclosure 22 by way of a suitable steam lineconnections 24, 26 there also being provided outlets (not shown) forcarry off of any steam condensate as well as water removed from thetobacco. During processing, a certain quantity of excess steam willescape enclosure 22 through cutoff tubes 20.

After the temperature condition of the microwave applicator has beenproperly equilibrated, tobacco is delivered from the hopper 12 onto thetraveling conveyor belt 14 and is transported through the microwaveapplicator wherein the tobacco is exposed to the microwave field and theliquid impregnant is evaporated with the pressure thereof and the rateof evaporation ex panding the tobacco cell walls and thus puffing thetobacco. As indicated earlier the present invention provides that thepuffing of the tobacco can be effected in a very short period of timeand without unduly heating the tobacco by employing a microwave field.Accordingly, the conveyor belt 14 is designed to operate at a speed totransport the tobacco through the oven so that the total time exposureof the tobacco to the microwave energy is within the range of about 0.05to about 5.0 minutes, but preferably in a time in the range of 0.05 to0.15 minutes. In conjunction with such exposure periods, the powerdensity of the microwave applicator is preferably in the range of about0.01 to about 2.5 kw but preferably 2.0 to about 2.5 kw.

As those skilled in the art will discern, the microwave field frequencycan be any one of the four bands available for the commercial purposesof treating vegetable material as provided under existing FCCregulations, such frequencies being 22,000; 5800; 2,450 and 915 MHalthough it will be understood that any frequency within the range of915-22,000 MH would be suitable for the practice of the presentinvention with frequencies at the higher end of the range beingpreferred. The maintenance of a water vapor containing zone whereinpuffing takes place is an important part of the present invention and ashas already been indicated the saturation of the zone defined by thehood enclosure 22 preferably is effected by using saturated steam. Thedegree of water vapor saturation within the zone should be such as toprovide a relative humidity therein in the range of 40-100 percent,relative humidities of somewhat higher values being preferred.

The fringing field applicator 30 depicted in FIG. 2 is as indicated aconventional type manufactured by the Genesys Systems, Inc., Palo Alto,Calif, and is connected to a microwave power source at the wave-inconnection 32 and at the wave-out end to a dummy load connection 34.

For the purposes of providing continuous uniform delivery of tobacco tothe microwave applicator unit, the tobacco from hopper I2 can belevelled on the conveyor belt 14 in known manner, as for example per useof a rotary brush mechanism, to provide a smooth bed of uniformthickness. Following the puffing of the tobacco in the microwaveapplicator, the product as it reaches the end of the conveyor belttravel at the right end of FIG. 1 can be removed for further processingin known manner. For example, the same can be blended with regular cuttobacco leaf filler for cigarette filler purposes or it can be used inits entirety as a cigarette filler. Further and since the puffing of thetobacco results in reduction of the moisture content of the tobaccobelow a desired level, it may be desirable to reestablish a particulardesired moisture content in the puffed tobacco, as for example toprovide a tobacco moisture content of about 8 to 15 percent.

The following examples serve to illustrate the present invention:

EXAMPLE 1 A cut, bright filler tobacco containing 40 percent O.V. wasfed to the conveyor belt. after the apparatus of FIG. 1 had been broughtto equilibrium temperature condition with steam. Three runs with varyingparameters gave the results shown in Table I below.

Table l Tobacco Power density feed rate Exposure time kw g./min. sec. 7!Expansion The degree of expansion was determined by measuring theapparent density of filler at -11 percent O.V. before and aftertreatment and dividing the first by the second. Apparent density wasmeasured by the standard weight-loss method on immersion in acetone.

EXAMPLE 2 Table II Microwave Control Treated Change Rod wt.. g. 0.8700.766 12 Rod firmness, 35.5 35.5 0 Rod resistance to draw, 2.9 2.8

in water Total particulate matter, 26.l 22.6 l3

mgJcig. Nicotine, mg./cig. l.79 L48 1? Water, mg./cig. 2.8 2.3 l8 Puffcount 9.5 8.5 II

Filler containing 20 percent O.V. was similarly treated. Expansion wasabout 15 percent.

EXAMPLE 3 Ten pounds of cut filler tobacco containing approximately 60percent O.V. was fed to the conveyor belt and passed through theapparatus (already brought to temperature with steam) at rates to giveexposure varying from 2 to 15 seconds, at power density from 2.0 to 2.5kw. Expansion of the product compared at about 11 percent O.V. is 30 to50 percent.

EXAMPLE 4 Cut bright filler containing 40 percent O.V. was treatedaccording to the process of Example 1, with particular attention beinggiven to keeping the stream of filler uniform. Power density was 2.0kw., feed rate 20g/min., exposure time 4.5 sec. Expansion was found tobe 43 percent.

Other forms of microwave energy generation may be used in the process ofthe present invention.

As indicated earlier, salt solutions can be employed as the impregnant.Water-soluble salts in general will give improved microwave couplingefficiency and thus somewhat better expansion than water. The salts mustbe chosen with regard to their effect on smoking characteristics sincethey will remain in the tobacco. Acceptable salts include Na, K, Ca, orMg citrates, acetates, sulfates and the like. Aqueous ammonia though nota salt also could be used.

The description of the present invention has been given herein in termsof an ambient pressure in the microwave applicator unit, e.g., oneatmosphere, although an overpressure also may be used effectively.

What is claimed is:

1. A process for puffing tobacco which comprises treating tobacco leafwith a water impregnant to provide said tobacco leaf with a moisturecontent, in the range of about 20 percent to about 60 percent by weightof the total weight of the impregnated tobacco leaf, introducing saidimpregnated tobacco leaf into a treating zone, flowing steam throughsaid treating zone to saturate said zone with water vapor to give apartial pressure of at least 40 percent and subjecting said tobaccowhile in said zone to a microwave field to vaporize the water in saidtobacco leaf at a rate and pressure which expands the cell walls of saidtobacco causing puffing of the same.

2. The process of claim 1 wherein the water impreg: nant is that presentin a salt solution.

3. The process of claim 2 wherein the salt in said salt solution issodium chloride and is present in the range of 0.1 to 0.7 mol.

4. The process of claim 1 wherein the water impregnant comprises about40 percent by weight of the total weight of the impregnated tobaccoleaf.

5. The process of claim 1 wherein said tobacco is exposed to saidmicrowave field for a time between about 0.05 minutes to about 5.0minutes.

6. The process of claim 5 wherein said tobacco is exposed to saidmicrowave field for a time between about 0.05 minutes to about 0.15minutes.

7. The process of claim 1 wherein said microwave field is generated at afrequency between about 915 MH and about 22,000 MH and is of a powerdensity of between about 0.1 kw to about 2.5 kw.

8. The process of claim 7 wherein said microwave field is of a powerdensity of between about 2.0 kw to is in cut filler form.

l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,842,846 Dated October 22, 1974 Inventor(s) 'I'j bgr Laszlo It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Col. 8, cancel lines 2 4.

Signed arid sealed this 29th day of April 1975 (SEAL) Attest:

' C. MARSHALL DANN RUTH C. MASON Conunissioner of Patents AttestingOfficer and Trademarks

1. A process for puffing tobacco which comprises treating tobacco leafwith a water impregnant to provide said tobacco leaf with a moisturecontent in the range of about 20 percent to about 60 percent by weightof the total weight of the impregnated tobacco leaf, introducing saidimpregnated tobacco leaf into a treating zone, flowing steam throughsaid treating zone to saturate said zone with water vapor to give apartial pressure of at least 40 percent and subjecting said tobaccowhile in said zone to a microwave field to vaporize the water in saidtobacco leaf at a rate and pressure which expands the cell walls of saidtobacco causing puffing of the same.
 2. The process of claim 1 whereinthe water impregnant is that present in a salt solution.
 3. The processof claim 2 wherein the salt in said salt solution is sodium chloride andis present in the range of 0.1 to 0.7 mol.
 4. The process of claim 1wherein the water impregnant comprises about 40 percent by weight of thetotal weight of the impregnated tobacco leaf.
 5. The process of claim 1wherein said tobacco is exposed to said microwave field for a timebetween about 0.05 minutes to about 5.0 minutes.
 6. The process of claim5 wherein said tobacco is exposed to said microwave field for a timebetween about 0.05 minutes to about 0.15 minutes.
 7. The process ofclaim 1 wherein said microwave field is generated at a frequency betweenabout 915 MHZ and about 22,000 MHZ and is of a power density of betweenabout 0.1 kw to about 2.5 kw.
 8. The process of claim 7 wherein saidmicrowave field is of a power density of between about 2.0 kw to about2.5 kw.
 9. The process of claim 1 wherein said zone is saturated withwater vapor by flowing saturated steam therethrough.
 10. The process ofclaim 7 wherein said zone is maintained at an equilibrated temperaturecondition in the range of between about 75C. and 150C., and any steamcondensate present therein is continuously removed therefrom.
 11. Theprocess of claim 7 wherein the temperature condition in said zone isequilibrated before introducing said tobacco leaf into said zone. 12.The process of claim 1 wherein said tobacco leaf is in cut filler form.